The present invention relates to an apparatus for finely working the outer circumferential faces of self-tensioning piston rings that are combined into a packet, with the rings lying under their inherent tension against the inner wall of a cylindrical sleeve and being arranged with slight axial spacing between two discs, and wherein the rings are rotated relative to the sleeve and moved back and forth, with at least one disc being pivotal.
In order to produce very smooth and geometrically accurate surfaces, piston rings are finely worked with special equipment. If the fine working is effected by lapping, the piston ring surface to be worked slides on a corresponding counterface of a lapping tool. A fluid containing a lapping agent is introduced between the two parts to produce a polishing or grinding effect.
German Pat. No. 1,216,730 discloses an apparatus in which piston rings, which are held together between two discs, are finely worked in a so-called lapping sleeve. The discs can be driven to rotate relative to the sleeve but cannot be tilted. During the lapping process, the individual rings are caused to rotate so that they are uniformly worked over their entire circumference. This process phase initially produces a smooth, cylindrically round lapped running face. However, piston rings often should have a convexly rounded running surface in their finished state, that is, the cross-sectional outline of the running face has an arcuate curve. In order to meet this requirement, the initially cylindrically round lapping running faces are lapped into the convex shape in an additional process step. Various methods can be employed to produce the convex running surface. One possibility is, for example, to cause the rings to perform a tilting movement within the sleeve.
For this purpose, German Pat. No. 1,250,759 discloses a clamping disc which is made tiltable in the rhythm of its rotary drive. The tilting movement of the clamping disc is generated by a sloped end face on a hollow shaft which surrounds the spindle of the clamping disc and against which the clamping disc spindle is supported at a frontal face that extends perpendicularly to the spindle axis. The magnitude of the tilting movement is here a function of the angle of the sloped face; that is, for every variation in convexity required for each series, a special hollow shaft must be employed. This involves high tool costs and incurs high retrofitting expenditures.